The idea that economics is a merely descriptive or value-free science can be taken in several different ways.
If we take it that economics as such does not make ethical conclusions, then this is simply part of the definition of economics. It cannot arrive at ethical conclusions because it does not proceed from ethical premises. Economics as such does not consider “justice” and “temperance,” though an economics contrary to these principles would be bad economics. Economics is bound by ethics, but does not have ethical conclusions.
In Wood’s book, he wants to go farther then this, suggesting that economics is a science like physics, devoid of value judgement and dealing with just facts. He offers the example of minimum wage. Economics does not say whether minimum wage laws are good or bad, but simply describes the consequences of such actions. This is true as far as it goes, but this is because of our previous point. The good or evil of minimum wage laws concerns politics and is a political conclusion. Economics as such cannot arrive at political conclusions, because it is not politics. So, whether minimum wage laws are good or not for the common good, economics is silent.
However, economics is not wholly silent upon the topic. While economics cannot conclude as to the common good as such, it can conclude to the economic common good. From economic premises, we can conclude that minimum wage laws will disrupt and harm the market and inhibit its ends, thus violating the common good of the economy. This is more than merely descriptive, but includes the value judgement that this bad economics. In a similar way, from economic premises, socialism is found to be wretched economics, in addition to be unethical and contrary to the common good.
Wood’s seems to miss the point that economics does have real and concrete ends that it considers. There is such a thing as good and bad economics. This is part of Bastiat’s point in his work on the hidden. It is bad economics to ignore the hidden. This is not an ethical or political judgement, but a economical one. Ignoring the hidden inhibits the production and management of wealth. One consequence of this is that there is a right way to do so and this constitutes a value judgement on the part of economics.